18 research outputs found

    Inter-specific interactions between carbon-limited soil bacteria affect behavior and gene expression

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    Recent publications indicate that inter-specific interactions between soil bacteria may strongly affect the behavior of the strains involved, e.g., by increased production of antibiotics or extracellular enzymes. This may point at an enhanced competitive ability due to inter-specific triggering of gene expression. However, it is not known if such inter-specific interactions also occur during competition for carbon which is the normal situation in soil. Here, we report on competitive interactions between two taxonomically non-related bacterial strains, Pseudomonas sp. A21 and Pedobacter sp. V48, that were isolated from a dune soil. The strains showed strong effects on each other’s behavior and gene expression patterns when growing together under carbon-limited conditions on agar. The most pronounced observed visual changes in mixed cultures as compared to monocultures were (1) strong inhibition of a bioindicator fungus, suggesting the production of a broad-spectrum antibiotic, and (2) the occurrence of gliding-like movement of Pedobacter cells. Two independent techniques, namely random arbitrary primed-PCR (RAP-PCR) and suppressive subtractive hybridization (SSH), identified in total 24 genes that had higher expression in mixed cultures compared to monocultures. Microbial interactions were clearly bidirectional, as differentially expressed genes were detected for both bacteria in mixed cultures. Sequence analysis of the differentially expressed genes indicated that several of them were most related to genes involved in motility and chemotaxis, secondary metabolite production and two-component signal transduction systems. The gene expression patterns suggest an interference competition strategy by the Pseudomonas strain and an escape/explorative strategy by the Pedobacter strain during confrontation with each other. Our results show that the bacterial strains can distinguish between intra- and inter-specific carbon competition.

    Draft Genome Sequence of Pedobacter sp. Strain V48, Isolated from a Coastal Sand Dune in the Netherlands

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    Pedobacter sp. strain V48 participates in an interaction with Pseudomonas fluorescens which elicits interaction-induced phenotypes. We report the draft genome sequence of Pedobacter sp. V48, consisting of 6.46 Mbp. The sequence will contribute to improved understanding of the genus and facilitate genomic analysis of the model interspecies interaction with P. fluorescens

    Quantitative detection and diversity of the pyrrolnitrin biosynthetic locus in soil under different treatments

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    The prevalence of antibiotic production loci in soil is a key issue of current research aimed to unravel the mechanisms underlying the suppressiveness of soil to plant pathogens. Pyrrolnitrin (PRN) is a key antibiotic involved in the suppression of a range of phytopathogenic fungi. Therefore, field soils from different agricultural regimes, including permanent grassland, arable land under common agricultural rotation and arable land under maize monoculture, were investigated in respect of the prevalence of pyrrolnitrin biosynthetic loci. Primers for detection of the prnD gene were used for initial PCR/hybridisation-based assessments. By this method, evidence was obtained for the contention that PRN production loci were most prevalent in grasslands, however, robust quantitative data were not achieved. To quantify the prevalence of PRN biosynthetic loci, we designed a TaqMan PCR system based on the prnD gene for the real-time quantitative detection of this production locus in soil. The system was found to be specific for prnD sequences from Pseudomonas, Serratia and Burkholderia species. Using pure culture DNA, the prnD gene was detectable down to a level of 60 fg, or approximately 10 gene copies, per amplification reaction. Application of the system to soil DNA spiked with different levels of Field soil samples obtained from the different agricultural regimes were then screened for the prevalence of prnD with the real-time PCR system. The quantitative data obtained suggested a strongly enhanced presence of prnD genes in grassland or grassland-derived plots, as compared to the prevalence of this biosynthetic locus in the arable land plots. The implications of these findings are placed in the context of the suppressiveness of soil to phytopathogens, notably Rhizoctonia solani AG3. [KEYWORDS: Pyrrolnitrin biosynthetic locus; Detection; Real-time PCR; Diversity; Soil]

    Effects of agronomical measures on the microbial deversity of soils as related to the suppression of soil-borne plant pathogens

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    The diversity of soil microbial communities can be key to the capacity of soils to suppress soil-borne plant diseases. As agricultural practice, as well as directed agronomical measures, are known to be able to affect soil microbial diversity, it is plausible that the soil microflora can be geared towards a greater suppressivity of soil-borne diseases as a result of the selection of suitable soil management regimes. In the context of a programme aimed at investigating the microbial diversity of soils under different agricultural regimes, including permanent grassland versus arable land under agricultural rotation, we assessed how soil microbial diversity is affected in relation to the suppression of the soil-borne potato pathogen Rhizoctonia solani AG3. The diversity in the microbial communities over about a growing season was described by using cultivation-based – plating on different media – and cultivation-independent – soil DNA-based PCR followed by denaturing gradient gel electrophoresis (DGGE) community fingerprinting – methods. The results showed great diversity in the soil microbiota at both the culturable and cultivation-independent detection levels. Using cultivation methods, various differences between treatments with respect to sizes of bacterial and fungal populations were detected, with highest population sizes generally found in rhizospheres. In addition, the evenness of eco-physiologically differing bacterial types was higher in grassland than in arable land under rotation. At the cultivation-independent level, clear differences in the diversities of several microbial groups between permanent grassland and arable land under rotation were apparent. Bio-assays that assessed the growth of R. solani AG3 hyphae through soil indicated a greater growth suppression in grassland than in arable land soils. Similarly, an experiment performed in the glasshouse showed clear differences in both microbial diversities and suppressiveness of R. solani growth in soil, depending on the presence of either maize or oats as the crop. The significance of these findings for designing soil management strategies is discussed. [KEYWORDS: microbial diversity, soil, pathogen suppression, molecular methods]

    Assessment of the diversity, and antagonism towards Rhizoctonia solani AG3, of Pseudomonas species in soil from different agricultural regimes

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    The genus Pseudomonas is one of the best-studied bacterial groups in soil, and includes numerous species of environmental interest. Pseudomonas species play key roles in soil, for instance in biological control of soil-borne plant pathogens and in bioremediation of pollutants. A polymerase chain reaction-denaturing gradient gel electrophoresis system that specifically describes the diversity of Pseudomonas spp. in soil was developed. On the basis of this molecular method as well as cultivation-based approaches, the diversity of Pseudomonas species in soil under different agricultural regimes (permanent grassland, arable land either under rotation or under monoculture of maize) was studied. Both types of approaches revealed differences in the composition of Pseudomonas populations between the treatments. Differences between the treatments were also found based on the frequency of isolation of Pseudomonas strains with antagonistic properties against the soil-borne pathogen Rhizoctonia solani AG3. Higher relative numbers of isolates either with antagonistic activity toward this pathogen or with chitinolytic activity were obtained from permanent grassland or from the short-term arable land than from the arable land. The results obtained in this study strongly indicate that agricultural regimes influence the structure of Pseudomonas populations in soil, with specific antagonistic subpopulations being stimulated in grassland as compared to arable land. [KEYWORDS: Pseudomonas; Bacterial diversity; Soil; Polymerase chain reaction-denaturing gradient gel electrophoresis; Antifungal activity]

    Predominant Bacillus spp. in agricultural soil under different management regimes detected via PCR-DGGE

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    A PCR system for studying the diversity of species of Bacillus and related taxa directly from soil was developed. For this purpose, a specific 24-bp forward primer located around position 110 of the 16S ribosomal RNA gene was designed and combined with a reverse bacterial primer located at the end of the gene. The specificity of this PCR system for bacilli and related taxons was confirmed on the basis of tests with diverse strains as well as with soil DNA. Analysis of a soil DNA derived clone library showed that the amplified fragments affiliated exclusively with sequences of gram-positive bacteria, with up to 95% of the sequences originating from putative Bacillus species. In particular, sequences affiliated to those of B. mycoides, B. pumilus, B. megaterium, B. thuringiensis, and B. firmus, as well as to related taxa such as Paenibacillus, were obtained. A minority, i.e., less than 6%, of the clones affiliated with other gram-positive bacteria, such as Arthrobacter spp., Frankia spp., and uncultured gram-positives. The amplified fragments were used as templates for a second PCR using bacterial 16S rDNA primers, yielding PCR products of about 410 bp, which were separated by denaturing gradient gel electrophoresis (DGGE). Amplicons indicating Bacillus spp. were found in the gel between 45% and roughly 60% denaturant, whereas those representing other, high-G+C% bacteria, were localized in gel regions with denaturant concentrations exceeding about 60%, thus allowing the distinction between these two groups of sequences. We applied this system to compare the group-specific diversity in bacterial communities in an agricultural soil under different regimes, i.e., permanent grassland, grassland recently turned to arable land, and arable land under agricultural rotation. Differences in the Bacillus-related community structures between the treatments were clearly detected. Higher diversities, as judged by Shannon–Weaver indices calculated on the basis of the molecular profiles, were consistently observed in the permanent grassland and the grassland turned into arable land, as compared to the arable land

    Draft Genome Sequence of the Antagonistic Rhizosphere Bacterium Serratia plymuthica Strain PRI-2C

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    Serratia plymuthica strain PRI-2C is a rhizosphere bacterial strain with antagonistic activity against different plant pathogens. Here we present the 5.39-Mb (G+C content, 55.67%) draft genome sequence of S. plymuthica strain PRI-2C with the aim of providing insight into the genomic basis of its antagonistic activity

    Predominant Bacillus spp. in agricultural soil under different management regimes detected via PCR-DGGE

    No full text
    A PCR system for studying the diversity of species of Bacillus and related taxa directly from soil was developed. For this purpose, a specific 24-bp forward primer located around position 110 of the 16S ribosomal RNA gene was designed and combined with a reverse bacterial primer located at the end of the gene. The specificity of this PCR system for bacilli and related taxons was confirmed on the basis of tests with diverse strains as well as with soil DNA. Analysis of a soil DNA derived clone library showed that the amplified fragments affiliated exclusively with sequences of gram-positive bacteria, with up to 95% of the sequences originating from putative Bacillus species. In particular, sequences affiliated to those of B. mycoides, B. pumilus, B. megaterium, B. thuringiensis, and B. firmus, as well as to related taxa such as Paenibacillus, were obtained. A minority, i.e., less than 6%, of the clones affiliated with other gram-positive bacteria, such as Arthrobacter spp., Frankia spp., and uncultured gram-positives. The amplified fragments were used as templates for a second PCR using bacterial 16S rDNA primers, yielding PCR products of about 410 bp, which were separated by denaturing gradient gel electrophoresis (DGGE). Amplicons indicating Bacillus spp. were found in the gel between 45% and roughly 60% denaturant, whereas those representing other, high-G+C% bacteria, were localized in gel regions with denaturant concentrations exceeding about 60%, thus allowing the distinction between these two groups of sequences. We applied this system to compare the group-specific diversity in bacterial communities in an agricultural soil under different regimes, i.e., permanent grassland, grassland recently turned to arable land, and arable land under agricultural rotation. Differences in the Bacillus-related community structures between the treatments were clearly detected. Higher diversities, as judged by Shannon–Weaver indices calculated on the basis of the molecular profiles, were consistently observed in the permanent grassland and the grassland turned into arable land, as compared to the arable lan

    Lessons from 1,3-Hydride Shifts in Sesquiterpene Cyclizations

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    Stereospecifically labelled precursors were subjected to conversion by seven bacterial sesquiterpene cyclases to investigate the stereochemistry of their initial 1,10-cyclisation-1,3-hydride shift cascades. Enzymes with products of known absolute configuration showed a coherent stereochemical course, except for (−)-α-amorphene synthase, for which the obtained results are better explained by an initial 1,6-cyclisation. The link between the absolute configuration of the product and the stereochemical course of the 1,3-hydride shifts enabled assignment of the absolute configurations of three enzyme products, which were confirmed independently through the absolute configuration of the common byproduct germacrene D-4-ol

    Rhizosphere microbial community and its response to plant species and soil history

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    The plant rhizosphere is a dynamic environment in which many parameters may influence the population structure, diversity and activity of the microbial community. Two important factors determining the structure of microbial community present in the vicinity of plant roots are plant species and soil type. In the present study we assessed the structure of microbial communities in response to four plant species (i.e. maize (Zea mays L.), oat (Avena sativa L.), barley (Hordeum vulgare L.) and commercial grass mix) planted in soil with different land use history (i.e. arable land under crop rotation, maize monoculture and permanent grassland). Both factors, plant species and land use history, showed clear effects on microbial community and diversity as determined by PCR-DGGE fingerprinting with universal and group-specific bacterial primers. Moreover, we explored the rhizosphere effect of these plant species on the abundance of bacterial antagonists of the potato pathogen Rhizoct! onia solani AG3. The data showed that the abundance and taxonomic composition of antagonists differed clearly between the different plants. The highest percentages of antagonists were found in maize and grass rhizosphere. When antagonistic Pseudomonas populations were compared, the highest, abundance and diversity of antagonists were detected in barley and oat rhizospheres, as compared to maize and grass rhizosphere. The results obtained in our study demonstrate clearly that plant species and soil type are two important factors affecting the structure of total bacterial, Pseudomonas and Bacillus community.
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